1. Field of the Invention
This invention relates to a process of treating aqueous condensate which has been formed as a result of the cooling of raw gas produced by a gasification of solid fuels by a treatment with gasifying agents which contain oxygen, water vapor and/or carbon dioxide under a pressure of 5 to 150 bars, which raw gas is cooled in at least one cooling stage.
2. DISCUSSION OF THE PRIOR ART
Such process has been described in German Offenlegungsschrift No. 2,543,532 and corresponding U.S. Pat. No. 4,065,273. It is also known to gasify solid fuels, particularly coal or lignite, with oxygen, steam or carbon dioxide as a gasifying agent, under a pressure of 10 to 150 bars. Suitable processes, in which the fuel is kept in a fixed bed and the incombustible mineral constituents of the fuel are withdrawn under the fixed bed as solid ash, are described, e.g., in Ullmanns Enzyklopadie der technischen Chemie, 4th edition (1977), volume 14, pages 383 to 386. Details of that known gasification process are apparent from U.S. Pat. No. 3,540,867 and U.S. Pat. No. 3,854,895. It is also known to gasify the fuel in a fixed bed in conjunction with a removal of liquid slag. This is disclosed in British Patent Specifications Nos. 1,507,905; 1,506,671; and 1,512,677.
The raw gas produced by the known process of gasifying in a fixed bed usually becomes available at temperatures between 300.degree. and 900.degree. C. and contains substantial quantities of water vapor and also products of dry distillation, such as tar, phenols, fatty acids, and ammonia. These accompanying substances are contained in the condensate which is formed as the raw gas is cooled, and they must be removed in various process stages. To that end, tar and oil are removed from the condensate, which is then subjected to an extraction of phenol, a removal of ammonia and finally to biological processing.
It is also known to gasify pulverized coal. In that case, no fixed bed is employed and the resulting raw gas is free from tar and oil and becomes available at temperatures up to about 1400.degree. C. Aqueous condensate is also formed as that raw gas is cooled.